Electron discharge device



May 19, 1953 D. BENEDICT 2,639,405

ELECTRON DISCHARGE DEVICE Filed Sept. 29, 1945 Sheets-Sheet 1 IN V EN TOR,

max/way D. L. BENEDICT ELECTRON DISCHARGE DEVICE May 19, 1953 3 Sheets-Sheet 2 Filed Sept. 29, 1945 mlmi y 19, 1953 D. L. BENEDICT 2,639,405

ELECTRON DISCHARGE DEVICE Filed Sept. 29. 1945' :s Sheets-Sheet 5 IN VEN TOR.

Patented May 19, 1953 ELECTRON DISCHARGE DEVICE Donald L. Benedict, Manhasset, N. Y., assignor to Sylvania Electric Products, Inc., a corporation of Massachusetts Application September 29,1945, Serial No. 619,289

16 Claims.

fields in the space between the anode and cathode.

Heretofore various types of electron discharge devices have been employed for producing ultra high frequency oscillations, one such type including an anode with a cathode spaced from the anode and with a magnetic means producing a field in the region between the cathode and anode, the direction of the magnetic field being substantially parallel with the axis of the electrodes and with an electric fieldpolarizing the anode positive with respect to the cathode. These general principles of such tubes which are commonly called magnetrons are discussed in numerous text books as Ultra High Frequency Techniques by Brainard, Koehler, Reich, and Woodruif (Van Nostrand), 1942 edition, pages 310-324.

It is to be noted that electron discharge devices of this type normally called magnetron tubes are of several kinds according to their performance, those most commonly encountered being the low field magnetron, the transit time magnetron, and the negative resistance magnetron. Of these the first two types have been adapted to use at ultra high frequencies, while the other is not commonly used at frequencies above cycles per second. The electron discharge device of the low field magnetron type, to which my invention finds efficient application, is characterized in-that the strength of the magnetic field applied to the tube ordinarily is lower than that which would be required to produce a rotational frequency of electrons equal to the circuit frequencies.

Included among those classes of magnetrons noted above are devices in which the anode is comprised of more than two pieces, such as the split type of anode magnetron described by W. Dallenbach in U. S. Patent 2,128,237, patented August 30, 1938. and the low field magnetron described by Haban and Gerth in U. S. Patent 2,151,912, patented March 28, 1939. Another type of high frequency electronic apparatus which employs ananode of a plurality of members is describedin Ramo -& Blewett, Patent No. 2,247,077, patented June 24, 1941. I

One of the difliculties, however, with electron discharge devices of the type mentioned above is v 2. that they are not arranged to operate over a controllable range in frequencies beyond that which may be obtained by the adjustment of the fields and the characteristics of the coupling device, such change being over a comparatively narrow range and at a considerable sacrifice of power generated as the frequency is made to deviate from that at which optimum performance for that particular device ,is attained.

It is therefore an object of my invention to provide an improved electron discharge device which employs magnetic and electric fields within the space between theanode and thecathode with an improved structure including a cavity resonator so that the device may be made to op- "erate efiiciently over a relatively wide range of frequencies.

-A further object of my invention is to provide an improved electron discharge device of the magnetron oscillator type which is tunable over a relatively wide range of frequencies and which is operable with relatively low electric and magnetic fields.

A still further object of my invention is to provide a tunable ultra high frequency magnetron which is relatively simple in construction and adaptable to quantity production.

A still further object of my invention is to provide a relatively simple tunable magnetron adapted to operate in a cavity resonator in which the frequency of operation is relatively independent of fluctuations in magnitude of the electric and magnetic fields.

Further objects and advantages of my invention will become apparent from the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawing:

Fig. 1 is an enlarged longitudinal sectional view through an electron discharge device embodying features of my invention and which'view is taken along the line I-l of Fig. 2;

Fig.2 is a transverse sectional view taken along the lines 22 of Fig. 1;

Fig. 3 is a top plan view of the cathode sleeve and part of Fig. 1;

Fig. 4 is a view partly in elevation, partly in longitudinal central section of the cathode sleeve employed in the construction of Fig. 1;

'5. Fig. 5v is an end view of the electron discharge deviceas looking from the top of Fig. 1 but drawn to'a much smaller scale;

Fig. 6 is a side view in elevation of one of the anode members employed in the construction of Fig. 1;

Figs. '7 and 8 are face and end views in elevation of a cavity resonator and its supporting means which is adapted to be employed with the electron device as illustrated in Fig. 1;

Fig. 9 is a fragmentary sectional view illustrating a modification of my invention with a cathode mounted slightly off center with respect to the anode;

Figs. 10 and 11 are fragmentary diagrammatic illustrations showing developmental views of the anode of further modificationsof my invention, Fig. 10 showing a finger on one of the members being longer than the others, and Fig. 11 show.- ing one of the fingers as'being" narrower than the others.

Fig. 12 is a sectional view along the lines I' -l 2 of Fig. '7 with certainof. the parts shown. infull, with themagneticmeans and the electrical means shown diagrammatically and. with the envelope partly broken away to illustrate more. clearly the internal parts thereof, and. Fig. 13, is a face view as seen from the underside oiv Fig. 12, the parts being shown-in section on the line It of Fig. 12.

Referring to the drawing, and more particularly to Fig. 1, I have illustrated an electron discharge device including an envelope made of any suitable material such as glass comprising three sections, the first section indicated by the nu meral I being the lower or header section. the central section being indicated by the numeral 2, and the top section or, dome section being indi cated by the numeral 3, the three sections ca-"ling separated by and sealed to discs 4 and 5 which may be formed of any suitable conductive ma terial such as oxygen-tree copper. the envelope there is provided a thermionic cathode 6 which is also provided with a heating element is which is supported within the cathode between ceramic members 8 and 9 Surrounding at least a portion of the cathode structure 8 I provide an anode structure which includes a first anode member Ill and a second anode member ll. As is illustrated more particularly in Fig. 6- each of the anode members includes a ring-like portion {Em with a plurality of fingerlike members, Nib, projecting therefrom substantiallyin the surface of a cylindrical shell. Each pbrtion Iiia, constitutes a circular connector for alternate conductive fingers Mb- In order to provide a convenient arrangement for supportingv the anode members, the anode member I 0 within the envelope is con nected to the disc member 1' through the ring member Eta. which is attached in any, suitable manner such as by. soldering to arrange portion l2 which is integral with thedi'sc'd andwhich extends internally of the envelope Lugs'l3 -may be provided for supporting'the ring against I the flange until it is soldered.

It'can also be seen rrom'an inspection of the drawing that the anode member H is similarly supported and connected to the lower disc memher 5. The anode members it and H are so formed and their extending fingers have such a length and width with respect to the space be tween adjacent fingers lllb that when they are positioned in the manner illustrated in Figs. 1

and 2,' they will be interdigitated or'intermeshed with substantially equal spacing between addecent fingers,'the fingers lyingin the surface of a'ri'ght circular cylinder with its axis 'subs'tantialv 1y coaxial with respect to the cathode axis. Any

.4 suitable number of digits may be employed for the anode, and in the illustrative embodiment of my invention each of the anode members has eight digits or fingers.

Any suitable arrangement may be provided for connecting the heater filament l to a heater circuit and in the arrangement illustrated in. the drawings I provide lead-in wires 14 and i t which may be made of any suitable alloy, such as chromium-nickel-iron alloy used for sealing to glass. The lead-in wires may be positioned in any desirable relation and as shown lead-in wire l l constitutes a' connection and a support through tabs l5 and l! for the cathode 5, and through a tab is for oneendzof the heater 5, while lead-in wire l5 and tab Ill constitute the connection and support for the other end of the heater.

The anode fingers may be interdigitatsd to any suitable amounts and in the arrangement illustrated in Fig. 1. they are. interdigitated over a part of their. length, the extremities being indicated by the planes 2lfandj2 l. The planes serve also to indicate the, approximate length of, the band of electron emissive'coating 22 ordinarily used onthecathode, but ins'ome' cases'the band is somewhat longer, while for a low power-or for continuous non-pulsed operation, it is frequently advantageous to make the coating band much shorter than that indicated by. the. planes 2% and 2 l.

Flanges 24. and 25 on the, cathode serve for the purpose of conserving the energy by. confiningthe electron discharge within the interdigitated region or" the-anode.

In order to provide a tunable resonantfcircuit which is. connected between the anode portions l8 and H I provide, as, illustrated in Figs. 12' and 13, a cavity resonator 2!; which. includes a boxlike portion 2'! and a plate, or, cover portion The envelopemay besupportedin the opening in the cavity with the discs against shoulders, a relatively tight connection being provided through a device during its operation I provide a concentric line including a tube 3.4 within which is contained a line 35 which connected at its inner looped end 35 to the cavity resonator.

When my electron discharge device is employed as is illustrated in the drawing a magnetic field is employed which magnetic field maybe produced in any. suitable manner such as through a magnet indicated generally by the numeral ill. As will be understood by those. skilled in the art the pole pieces of the magnetproduce a magnetic field which is substantially. parallel with the longitudinal axis of the anode and cathode. An electric field is provided through a source of direct current power indicated by the numeral 38, the positive side being connected to the cavity resonator through a conductor 39 and the negative side is connected to the cathode through a line 4t. A source of heater power for the oaths-dc heater 7 may be obtained from a source of power through the heater supply transformer 45.

In order to provide an arrangement for varying the tuning of the electron discharge device a plurality of tuning screws' tt is provided each of in the two .parts or the cavity resonator 26. It will be noted in the illustrative embodiment of my invention seven tuning screws are placed at 45 intervals except that where the lineso is fitted into the cavity resonator there is no tuning screw at this position. It will be understood however that both the form and number of the tuning screws may be varied to suit such factors as de' sign details of the tube in relation to the cavity resonator dimensions hence, for example, I may use five or nine screws and may place on the inner end another block which may contact the up per and lower ends of the cavity either conductively or insulatingly; or I may use other forms the magnetic field resulting in the precession of the electrons in one direction about the cathode. As the electrons approach the anode their velocity increases butdue to the action or the magnetic field their motion is substantially tangential to the inside cylindrical surface of the anode. Thus all the electrons in the vicinity of the anode tend to move in the same direction with high velocity and are in position to he acted upon by the high frequency electric field which exists between adjacent fingers of the anode. The influence of this high frequency field causes a bunching action of the electrons into spaced groups. These spaced groups tend to precess about the cathode with such phase and angular velocity as to be opposed by the instantaneous fields between adjacent teeth of the anode and thus to deliver high frequency power to the anode system.

There are several diiierent modes or ways in which oscillation may take place within the device. In the simplest mode, or 7r mode, to be described later, there are half as many groups of electrons precessing around the cathode as there are fingers on the anode. The angular velocity of rotation in radians per second of a group of electrons is Output irequency 41r Number of fingers in the 1r mode of oscillation, just mentioned, all of the fingers in one group such as those connected to the anode member ida are simultaneously at one potentiaLwhile all the fingers in the other group, such as those connected to the anode member lib are simultaneously at another potential. The potentials of the two-.groupsvary sinusoidally with respect to each other at the,

flow of electric current from one set of fingers i through the corresponding disc such ass through the cavity resonator, backthrough disc 5 and onto the other set of fingers that constitutes the high frequency oscillation in the cavity resonator.

5 In this mode of oscillation current flows radially direction of flow, of course, reverses itself at twicev the frequency of the output. At any instant in time within the cavity resonator the electric field strength due to instantaneous difierence in potential between the top and bottom of the cavity resonator is substantially independent of the angular position about the anode axis. The electric field strength at any instant is zero at the outer periphery of the cavity resonator space and increases monotonically in absolute value toward the anode. The 1r mode is the first of a series of radial modes, a radial mode being one in which there is no substantial variation in the instantaneous electric field with angular position about the cathode. Other radial modes may becharacterized by instantaneous potentials along the radius which start at zero in the periphery of the cavity resonator space, increase to a maximum in absolute value, decrease substantially to zero, and then increase to a high absolute value at the anode. Theoretically there may be any number of such maxima and substantially zero field points along a radius depending upon the radius of the cavity resonator used.

In order to minimize dielectric loss in the glass envelope walls it is desirous in some cases to operate at or nearthe harmonic of the free resonant frequency of the device in which case there will be more than one current loop in the circuit, and the tube walls which are sealed to the discs 4 and 5 may be placed at such a location in the system that they are removed from the voltage loops or at a point of minimum potential difference.

I have found at least one more important mode which is characterized by a dependence of the electric field structure in the cavity resonator upon the angular position about the cathode. In fact at any instant of time and progressing about the cathode axis in a circular path within the cavity resonator, the electric field starts at zero, increases first to a maximum, decreases to zero, changes polarity and decreases to a minimum in the opposite direction, then increases to zero at the point of beginning. I have found in this mode of oscillation that it is possible to attain a higher frequency witha given cavity resonator and to obtain greater power output at a given frequency of oscillation than is possiblewith the 1r mode. It is also possible to operate the tube in such a manner that in a circular path about the cathode in the cavity resonator the instantaneous field strength will be found to pass through two maxima and two minima or any even integral number of maxima and. minima.

It will thus be seen that in the first mode of oscillation characterized by an angular dependence of the field strength that the number of electron groupings precessing about the cathode due to the magnetic field cannot be half the number of anode fingers but must be either one 7 favorable transfer Qf power to the coupling loop- Power ma be cou l out o th ca i r s n to b an suita l evic a d I have llu e in the drawings an arrangement for coupling out power which includes a loop which extends into an opening in the periphery of the cavity resonator. The coupling loop is inductively coupled to the magnetic field set up in th cavity resola-t by e os llat I thereiore find it desirable to provide my electron discharge device with any suitable means so that the voltage and current loops may be provided in a predetermined location in the cavity resonator with this mode of operation and with respect to the position of the coupling loops andby placing the line to remove power at that portion of the cavity resonator where there is a rel ively large change of magnetic flux, I will thereby be able to obtain an optimum transfer of power from the cavity resonator to the line.

Any suitable structural arrangement may beeznplo-yed for producing this asymmetry and in Eligs. 9, lo, and 11 I have illustrated three possible arrangements for producing this asymmetry. Thus in Fig. 9 I have illustrated the cathode 6a which has been displaced from its position of being substantially coincident with the longitudinal axis of the interdigitated anode or in other words the cathode 6c is shifted to the right as illustrated in Fig. 9. In Fig. 10 I have illustrated an arrangement for producing asyr. metry which includes an anode construction in which the various fingers have substantially the same size and shape except one of the. fingers t5 on one of the anode portions is longer or extends to a closer position to the ring Another method of producing the asymmetry is illustrated in Fig. ll in which one of the fingers of one of the anode members is narrower than the other fingers. The forms in 9-11 involve a construction that departs in a predetermined manner from circular symmetry thus being circularly asymmetric. These disclosed forms are generally circularly symmetric. This symmetry is to be distinguished from endwise symmetry that may or may not be present.

It will be understood that many other types of mechanical asymmetry may be employed so as to predetermine the position of the voltage nodes and loops in the construction with respect to the power loop, such, for example, by providing the asymmetry in the external cavity resonator. Thus with a cavity resonator tuned by several radial screws spaced at 45 intervals and with the power output loop located in the 8th radial position, the power output of the device may be improved by withdrawing one or both of the screws 43a, (indicated in Figure 13) on the cavity resonator diameter perpendicular to the radius passing through the coupling loop and such screws may be completely removed with resulting improvement in the power output in certain cases provided all the other screws are kept in substantially the same radial distance from the center of the cavity resonator.

Any suitable method or arrangement may be employed for positioning the power coupling loop. with respect to the asymmetry of the device, the maximum change of magnetic field, or the current or voltage loops. Thus when the asymmetry is obtained by moving the cathode sothat its axis is not in coincidence with the axis of the anode, the power coupling loop should be n ith the d r o of m e nt o the cathade to. pr duc he ymme ry h t e asynnnetry is produced by two larger fingers dimetr cal opp ite e c other, hen the o in oo sh d be end cular to a plane passing through the larger fingers. In any case the predetermined position of the coupling loop with respect to the asymmetry or the point of maximum change of flux or the point of the voltag node may be obtained by rotating the envelope within the cavity resonator until it attains that position with respect to the cavity resonator that a maximum or optimum amount of power is withdrawn through the coupling loop.

Although I have shown and described partieular embodiments of my invention, I do not desire to be limited to the embodiments described, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim is:

1. An electron discharge device adapted to be connected to an encircling cavity resonator and to operate as a magnetron, comprising a cathode elongated along an axis, and anode means surrounding said cathode and exposed in substantially all radial directions to said cathode, said anode means including continuous encircling terminal rings for connection to an encircling resonator, a pair of connectors about said cathode and a plurality of like axially extending conductors joined together in alternation by a respective one of said connectors, the foregoing construction being generally mechanically circularly symmetric about said axis and incorporating a circularly asymmetric structure.

2.. An electron discharge device in accordance with claim 1 wherein said asymmetric construction is in the form of eccentricity of said anode means with respect to. said cathode.

A magnetron including a cathode, anode means exposed in substantially all radial directions to said cathode and including a plurality of connectors about said cathode, a plurality of conductors extending from each of said connectors with the conductors on each connector interposed between the conductors on the other of said connectors, a cavity resonator encircling said anode means and joined to said connectors, and output coupling means penetrating said cavity resonator, said magnetron being capable of operation in a mode providing stationary nodal points spaced about said connectors, the foregoing construction incorporating a circularly asymmetric structure fixing said nodal points in relation to said output coupling means.

4. A magnetron including a. cathode and coaxial anode means, said anode means including a pair of end connectors about said cathode and a plurality of like axially extending conductors spaced from each other and forming a cylinder, said conductors being joined alternately to a respective one of said end connectors, said con ductors being alike in dimensions and mutual spacing, said anode means additionally including a distinctive conductor which is irregular in some way with respect to said like conductors.

5. A magnetron in accordance with claim 4 wherein said distinctive conductor is larger than the other conductors and positioned in said cylinder.

A. ma netr n. i ac rdance i h im 4 h r n. s id dist n ti e n uc r i lon r th the oth r on c rs, and po iti ne in said cylndex.

A. magne ron. including c ax al. node. an cathode means, said anode means including a pair of circular connectors spaced axially apart and a plurality of like parallel conductive fingers spaced from each other and forming a cylinder, said fingers being'joined in alternation to a respective one of said circular connectors, said fingerslon each of said connectors extending toward the other connector and being alike in dimensions and mutual spacing, said anode means additionally including a conductor which is larger than said parallel conductive fingers, a cavity resonator encircling said anode means and joined to said circular connectors, and an output coupling element fixed in relation to said larger conductor.

8. A magnetron according to claim 3, wherein the circularly asymmetric structure is provided in the form of devices extending inwardly from the wall of said cavity resonator, certain of said devices extending further inwardly than the others.

9. A magnetron according to claim 3 wherein the circularly asymmetric structure is provided in the form of regularly spaced devices extending inwardly from the wall of said cavity resonator, said devices extending substantially equally except for a device spaced from said output coupling means by 90.

10. A magnetron including a cathode elongated along an axis, and anode means surrounding said cathode, said anode means including a pair of circular connectors coaxial with and surrounding said cathode, said circular connectors being separated from each other axially, said anode means'additionally having a plurality of axially extending conductors joined together in alternation by said circular conductors respectively, one of said axially extending conductors being different in width from the adjacent axially extending conductors.

11. A magnetron including a cathode, anode means expo-sedin substantially all radial directions to said cathode and including a plurality of connectors about said cathode, a plurality of conductors extending from each of said connectors with the conductors on each connector interposed between the conductors on the other of said connectors, a cavity resonator encircling said anode means and joined to said connectors, and output coupling means penetrating said cavity resonator, said magnetron being capable of operation in a mode providing stationary nodal points spaced about said connectors, the foregoing construction incorporating a circularly irregular structure fixing said nodal points in relation to said output coupling means.

12. A magnetron including a cathode and coaxial anode means, said anode means includin a pair of end connectors about said cathode and a plurality of like axially extending conductors spaced from each other and forming a cylinder, said conductors. being joined alternately to a respective one of said end connectors, said conductors being alike in dimensions and each substantially equally spaced from an adjacent one, said anode means additionally including a distinctive conductor which is irregular in some way with respect to said like conductors.

13. A magnetron in accordance with claim 12 wherein said distinctive conductor is larger than the other conductors and positioned in said-cylinder.

10 14. A magnetron including coaxial anode and cathode means, said anode means including a pair of circular connectors spaced axially apart and a plurality of like parallel conductive fingers spaced. from each other and forming a cylinder, said fingers being joined in. alternation -tola respective one of said circular connectors,

larger conductor.

15. A magnetron including a cathode and coaxial anode means, said anode means including a pair of end connectors about said cathode and a plurality of like axially extending conductors spaced from each other and forming a cylinder, said-conductors being joined alternately to a, respective one of said end connectors, said conductors being alike in dimension and each substantially equally spaced from an adjacent one, said anode means additionally including diametrically opposite conductors which are larger than said like conductors.

16. A magnetron including coaxial anode and cathode means, said anode means including a pairof. circular connectors spaced axially apart and a, plurality of like parallel conductive fingers spaced from each other and forming a cylind'er, said fingers being joined inalternation to a respective one of said circular connectors, said fingers ,on each of said connectors extending towa'rdthe other connector and being alike in dimensions and each substantially equally spaced from an adjacent one, said anode means additionally, including a pair of diametrically opposite conductors which are larger than said par- "allel conductive fingers, acavity resonator encircling said anode means and joined to said circular connectors, and an output coupling element in said resonator in a plane perpendicular to the plane of said diametrically opposite larger conductors.

DONALD L. BENEDICT.

References Cited in the file of this patent UNITED STATES PATENTS 

